1. Field of the Invention
The present invention relates to optical circuits and, more specifically, to printed circuit board assemblies having optical circuit components.
2. Description of the Related Art
A modern telecommunications or computer system typically has a number of printed circuit boards (PCBs) or cards, which plug into a backplane or motherboard. The backplane generally provides power to the PCBs and a pathway by which the PCBs communicate with each other. For most backplanes, an electrical bus, which is typically a series of wires, is a primary means by which the communication between the PCBs takes place. Electrical transmission characteristics of the bus are defined by its material properties, the physical layout of the components, the clock speed of the signals, etc. As complexity of telecommunications and computer systems increases, signals within backplanes are driven at increased clock speeds. However, at relatively high clock speeds (e.g., over 1 GHz), the performance of electrical buses may become unsatisfactory due to dispersion, crosstalk, and emission of and susceptibility to electromagnetic radiation.
To overcome this problem, backplane systems in which signals are transmitted through backplanes via both electrical and optical buses have been proposed. For example, one such backplane system is disclosed in U.S. Pat. No. 6,005,991, the teachings of which are incorporated herein by reference. However, one problem with optical backplane systems is that relatively accurate alignment is required to properly couple light between the backplane and the PCBs plugged into that backplane. For example, an optical bus of the backplane has to be sufficiently well aligned with the corresponding optical pathways and/or optical devices of the PCBs to provide reliable operation when the system is subjected to mechanical vibrations and/or temperature-induced deformations. In addition, backplane and PCB manufacturing tolerances that are typically less stringent than the required backplane/PCB alignment precision have to be appropriately accommodated.